The backdrop comes with an aluminium 50mm diameter tube. From the instruction, it appears to me that it was meant to be on another tube.
With the insight, ideally, it would have been better to buy three separate mounts and put them at the distance necessary for each backdrop.
50mm diamater (inside is around 48mm) is perfect for those wall mounts. However I say ideally, because for how the wall is made, I cannot put them closer than 2.5m between each other.
Therefore I had to find a solution to be able to mount the backdrop. This has been a pain, the reason is that obviously pipes come in standard size. Optimally I would have needed something between 45mm and 48mm but the closest was 40mm!

40mm is too small for those wall mounts, so I had to buy another 50mm pipe and join it with the 40mm to use as inside pipe for the backdrop.

It was a lot of work to reach a solution that didn't look flimsy, however I rather use a proper solution. What am I missing? Was the backdrop assuming that the wall mounts were at 2 meters between each other? Is there a standard pipe to use in photography for there cases? Or they assume that people mount these backdrop in those flimsy and cheap stands?

OK - IF I understand the above. You have two triple backdrop brackets made to fit 45-48mm tubes. These are 2.5m apart on the back wall but the supplied backdrop has a tube that is less than 2.5m long so you had to build an extension to allow the tube to fit between the brackets?

B = Bracket
E = Extension
One is shown extended, the other is show as supplied before extension.

When I had studio space many years ago I mounted the Manfrotto hooks on the wall wide enough apart to hold a standard roll of background paper (around 8' wide). I then purchased from the hardware store standard copper piping of the required length to hold the paper rolls (9' would suffice). The rolling down and up of the background paper was a manual process and required a step stool or short ladder; but it worked and was inexpensive. I still have the hooks somewhere in storage.